“This is inexplicable and tragic,” Manne Björnsson, head of Viaredssjön's sailing society and a friend of the family, said to local newspaper Borås Tidning.
The accident occurred on Saturday afternoon in Viaredssjön, a lake by Sandared in south-western Sweden.
Emergency services received an alarm call at 2.43pm, about a man and a boy floating in the water.
The little boy managed to get to shore on his own, but his father was still lying some 80 metres out in the water when emergency services showed up.
The water in the lake is still very cold.
“I don't know exactly, but it's no more than seven or eight degrees,” said the emergency services' Thomas Gunnarsson to Borås Tidning.
How the accident occurred remains a mystery. The man and his son headed out in their dinghy, both wearing life jackets.
The deceased man was also a competent sailor, explains Manne Björnsson, and even a leader of the lake's sailing society.
“The boat must've turned over somehow. It's completely inexplicable. I don't understand anything.”
The Borås police force is also unsure of how the accident occurred, but don't suspect that any crime has been committed.
“This is a tragic accident,” said police officer Johan Novenius.